The present invention relates generally to a bidirectional digital signal transmission system for transmitting bidirectionally digital signals such as digital video signals, audio signals, control signals and others by using a single transmission line (cable). More particularly, the invention is concerned with a repeater apparatus installed on the transmission line in such bidirectional digital signal transmission system.
The television camera system employed, for example, in the broadcasting field is generally comprised of a camera head unit for converting optical images into electric signals and a camera control unit for controlling the camera head unit by shaping and processing the electric signals appropriately.
To this end, a video signal, an audio signal (or speech signal) and others generated in the camera head unit are transmitted from the camera control unit to the camera head unit, whereas video signals for monitoring, audio or speech signals for communication are transmitted to the camera head unit from the camera control unit.
The signals mentioned above can be transmitted by using a coaxial triplex cable known as the triax cable. In that case, the aforementioned signals have to be multiplexed. Heretofore, these analogue signals are modulated and multiplexed on a frequency division basis for realizing the bidirectional transmission.
An object of the present invention is to provide a bidirectional digital signal transmission system for transmitting and receiving digital signals each containing video information and audio information substantially in realtime from both ends of a single transmission line and a repeater apparatus for extending a transmission distance in the bidirectional digital signal transmission system.
Another object of the invention is to provide a repeater apparatus which is so arranged that internal circuits thereof do not form a feedback loop for the signals transmitted from both ends of the transmission line.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to an aspect of the present invention a bidirectional digital signal transmission system which includes a transmission line and video instruments connected to the transmission line at both ends thereof, respectively, wherein in each of the video instruments, a digitized signal is multiplexed on a time division basis and compressed in a time base, whereby a transmission signal constituted by repetition of a signal period and a quiescent period is generated, and wherein the transmission signal generated by one of the video instruments is transmitted during the quiescent period of the transmission signal generated by the other video instruments to thereby realize a bidirectional digital signal transmission. The system includes a repeater apparatus inserted in the transmission line at an intermediate location thereof for compensating for deterioration of the signal brought about by the transmission line. The repeater apparatus includes a switch unit for preventing a transmission signal feedback loop from being formed internally of the repeater apparatus.
Furthermore, according to another aspect of the present invention, there is provided a repeater apparatus for a bidirectional digital signal transmission system in which digital signals each containing video information and audio information are transmitted alternately from both ends of a transmission line periodically at a predetermined interval for allowing the digital signals to be transmitted and received, respectively, at both ends of the transmission line substantially on a real time basis. The repeater apparatus is disposed on the transmission line and includes a first compensation circuit for compensating for deterioration of a first digital signal transmitted from one end of the transmission line to the other end, the deterioration being brought about by the transmission line, a second compensation circuit for compensating for deterioration of a second digital signal transmitted from the other end of the transmission line to the one end, a control circuit for detecting at least one of the first digital signal and the second digital signal to thereby generate a control signal, and a switch unit for selectively opening/closing a signal path for one of the first compensation circuit and second compensation circuit in response to the control signal.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings. dr
In the course of the description which follows, reference is made to the drawings, in which:
FIG. 1 is a schematic block diagram showing a basic arrangement of a bidirectional digital signal transmission system having a repeater apparatus according to an embodiment of the present invention;
FIG. 2 is a block diagram showing a system configuration of a bidirectional transmission system according to the present invention;
FIG. 3 is a block diagram showing a structure of a line-interface circuit employed in the bidirectional transmission system shown in FIG. 2;
FIG. 4 is a waveform diagram illustrating formats of signals transmitted in the bidirectional transmission system according to an embodiment of the invention;
FIG. 5 is a block diagram showing a structure of an repeater unit according to an embodiment of the present invention;
FIG. 6 is a block diagram showing a configuration of a bidirectional digital signal transmission system employing a repeater unit according to another embodiment of the present invention; and
FIG. 7 is a signal waveform diagram for illustrating operation of a repeater/transmission system according to an embodiment of the invention.